In the discussion that follows, reference is made to certain structures and/or methods. However, the references should not be construed as an admission that these structures and/or methods constitute prior art. Applicants expressly reserve the right to demonstrate that such structures and/or methods do not qualify as prior art.
Many industries have moved to layered materials to take advantage of the increased material characteristics and functionality provided by such composite materials. A simple example is the weather protection that paint provides for the strength that steel provides. A complex example is the miniature fluid channelling and micro reaction chambers made possible by bonding layers of etched and cut planar sheets of appropriate materials. Another complex example is the production of multiple layer printed circuit boards allowing much more complex circuits than were ever possible with single or dual layer materials. Another example is the bonding of supporting layers to delicate fabrics thereby increasing their durability without sacrificing texture and visual appeal. An example of a layered multi-functional device is the “SMART” card wherein many layers incorporating graphics, electronics, magnetics, and tactile features are incorporated into the one multi-layered device.
Much effort has been put into developing new processes to facilitate higher productivity and lower cost manufacturing of such composite layered materials. Over time, two streams of basic process engineering have developed. One method has concentrated on individual devices and streamlined the processes to layer or laminate complexity and/or functionality. The other method has concentrated on mass production of a long layered sheet from which individual devices are excised after modification.
Each of these methodologies have their advantages. The first methodology allows materials and devices of high complexity to be manufactured, but at high cost. The other methodology allows materials and devices to be mass produced at a lower cost, but with a concomitant reduction in complexity.
Further deficiencies and impediments in these methods create production compromises which further hinder attainment of the goal of low cost mass production of complex layered devices. Attempts have been made to combine these processes to achieve these aims but with varying and limited success.
Polymers have been used as a cheaper alternative to metals for manufacturing consumable devices especially since the 1940's and have been used for mass producing complex materials and devices for instrumentation since the early to mid 1990's. Since the use of polymers in low cost mass production is predominant, this discussion concerns the use of polymers, but applies equally to the use of other materials, including metals, metal oxides, metal foils, ceramics, glasses and thin or thick film surface coatings of these materials or combinations of them.
As well as the two main general process methodologies discussed above, surface feature fabrication techniques developed in the latter part of last century generally can be classified into two further categories.
The first is using direct machining methods in which the pattern of desired features is created directly on the surface of a stratum made of a suitable material. These methods include micromilling, laser based lithography and beam scanning, plasma etching, wet chemical UV lithography using photoresists, soft lithography, x-ray lithography and print-head deposition. Of these techniques, laser based processes have shown the most development due to the ease of processing and their ability to generate spatially confined sub-micron sized anisotropic features in a variety of materials.
The second methodology involves processes that use a master template to form the desired pattern. These feature replication processes, including soft lithography, embossing, compression molding, thermoforming, injection molding and reaction injection molding, and are particularly suitable to use with polymers, although these techniques are used with other materials including low melting point metals and frits.
Most of these approaches to materials or device fabrication are limited to creating 2-dimensional or 2%-dimensional structures. The most common of these approaches use one or more of Computer Numerical Control (CNC) micromilling, injection-molding or hot embossing, which can generate only very limited feature complexity. For the fabrication of complex 3-dimensional polymeric parts these micro-structuring methods typically require the assembly of several separately produced parts. However, these are serial fabrication processes that have alignment challenges when assembling micro-parts which lead to further labor-intensive processes with relatively low throughput and high associated production costs.
Another recent approach to the fabrication of complex polymeric materials and devices is the stacking, aligning and bonding of several layers of thin, already fabricated strata (films). This layered approach allows the use of relatively simple 2-dimensional manufacturing techniques (such as embossing, die cutting, and laser processing) as well as established bonding technologies to create complex 3-dimensional materials or devices. Such a 3-dimensional design approach is especially suited to high-volume manufacturing using reel-to-reel processing as described by Mehalso (“The Microsystems Road in the USA,” Mstnews, Volume 4/02, pp. 6-8 (2002)) and Schuenemann et al. (“Packaging of Disposable Chips for Bioanalytical Applications,” IEEE Electronic Components & Technology Conference, Nevada, USA (2004)).
Market pressures have prompted the development of mass manufacturing strategies away from traditional fixed production line approaches and towards flexible and responsive manufacturing systems to provide speed and rapid adaptation to meet market demands. This new manufacturing approach has typically been applied towards individual machine flexibility, or where discrete parts are produced on an assembly line, towards flexibility in redirecting or reordering the various production line modules. However, this is a more difficult proposition for reel-to-reel systems where the production line is a continuous process. Although U.S. Pat. No. 4,805,111 describes a modularized web system that can allow reconfiguration of the line, the flexibility of the system and the complexity of the produced devices are limited due to the continuous nature of the supply feed of the source materials when the system is in use.
To date, for layered polymeric device production, only batch, serial or continuous reel-to-reel processing techniques have been described.
In a typical batch process a large quantity or a number of products are fabricated in a single batch by a serial sequence of processes. In micro-technology, batch processing is very common in the fabrication of silicon or glass-based devices. An example is the fabrication of an integrated circuit, in which a silicon wafer is used as the substrate, and is subjected to a number of subsequent subtractive and additive techniques to form electronic parts such as gates and transistors within or upon the surface of the substrate. After these processing steps are completed, the devices are separated and packaged. In another batch process example, polymer bank notes are printed using a printing principle in which sheets or coupons containing several tens of notes are processed simultaneously and then separated in a final process step. Recent techniques combine this printing principle with the embossing of anti-counterfeiting micro-features into the surface of the polymer notes.
These batch manufacturing technologies, however, are rather expensive, especially when involving micro-features. The main industrial applications of devices made according to such methods are in high-throughput-oriented products in large industrial, scientific and governmental laboratories where the component can be reused, therefore the cost is amortized over the device's operational lifespan. For many potential applications of miniaturized layered bio-analytical devices, especially in disposable parts for point-of-care/point-of-use devices, such high production costs cannot be justified.
Batch-based fabrication of layered polymer based devices can be, and is, used to form multiple miniaturized devices through a sequence of processes, such as die cutting, bonding, milling and laser cutting. However due to the technical challenge of miniaturization and the need for such devices to reliably interface to real world samples and instruments, layered polymeric devices made this way are typically larger than their silicon or glass counterparts and provide unique packaging challenges. Furthermore, these batch-based processes can be difficult to automate, making the storing, handling, aligning and assembling of the produced micro-parts a commercial and technical challenge in itself. Consequently the number of devices that can be economically fabricated in parallel from a polymer batch-based process is restricted, making this method suitable for only low volume production.
Serial manufacturing is a manufacturing strategy in which manufacturing processes interact with a succession of single work pieces (or a very small number of work pieces). Examples are injection molding, hot embossing, or mechanical milling. Whereas each of these processes, widely used in industry, are optimized for high throughput, and several automation strategies to link serial processes are well in place for conventional products, the cycle times, the complexity and the cost of the necessarily highly automated process sequences all increase significantly for micro-structured devices. Storing, handling, assembling and aligning micro-parts in a competitive industrial environment remain the technical and economical challenges. Serial manufacturing processes are therefore best for small to medium-size production series.
A promising alternative to batch and serial manufacturing techniques are reel-to-reel, or so called web-based, processes. These are high-throughput production processes for combining composite polymer laminates used commonly in the packaging and printing industries, and have recently been described for complex layered device fabrication See Mehalso and Scheunaman et al., discussed above. See, also, U.S. Pat. Nos. 6,803,019 and 6,878,345.
The process according to the present invention utilizes flexible strata (films) continuously fed from reels containing the individual devices which are therefore fabricated on a continuous substrate. The fabricated devices can then be used either on a reel in a similar manner as described in U.S. Pat. Nos. 6,803,019 and 6,878,345, or divided into their individual parts, as described by Mehalso, discussed above.
Such web-based production lines tend to be highly automated and therefore very labor-efficient. The main advantage of processing on such a continuous automated system is the high throughput that can typically be achieved at a relatively low cost. Although initial investment costs for a web-based production line are higher than for serial production, manufacturing costs per product can be very low for a suitable large-scale production line.
The main disadvantage of such reel-to-reel production lines is that they are typically very sensitive to process variations. If a single processing component on the line goes out of tolerance or fails, then, due to the continuous nature of the production line, all parts passing that point are affected and production is effectively curtailed. Stopping the line to fix the problematic part causes the entire production run to come to a halt.
The lines are typically dedicated to one specific product, and require large investments in setup time and optimization of parameters, particularly when dealing with the tight tolerance requirements for devices with micro-features. Due to this setup time, the lengths of the web systems and the total effect of misalignment due to wear and tear or component failure, there is typically a lot of material waste. Commercial systems typically allow for this waste as a fixed percentage add-on cost and the end price of the product is varied accordingly. Another disadvantage of a reel-to-reel system is that the slowest process in the system limits the speed of the whole production system.
Furthermore, the substrates in a reel-to-reel process need to be flexible to allow for the reel handling systems. See, for example, U.S. Pat. No. 6,827,906. This limits the thickness of the layers used and the number of layers that can be combined and still be handled in such a production line. This presents problems for many layered material applications that require larger interfaces to the environment, larger fluid capacities, large handling structures, or a higher degree of component strength, or large numbers of bonded layers all of which characteristics tend to make the resultant device very rigid and therefore severely restrict the suitability of a reel-to-reel production method.
Another disadvantage of reel-to-reel handling systems is that the substrates need to remain in a mostly planar form with external surfaces having little or no protuberances. As the substrate thickness is also limited by this method, this imposes further design constraints on the product, which often require larger 3-dimensionally shaped objects to provide functionality, such as interfacing to an external device or the provision of internal liquid storage compartments.
The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.